text:
What is this turbine engine panel that opens on landing?
Tonight I flew from Munich to Dortmund on an A319 and I happened to sit just above the wings and turbine on the right side. Upon landing, the turbine opened a window or panel which exposed some grid like structure inside it and just a few seconds later, after touchdown, closed it again. Could someone explain to me what that is, how it is called and what its purpose is?

What you saw is the thrust reverser of the engine, which redirects some of the airflow forwards and therefore helps slowing the aircraft down. The grid like structure are the cascade vanes. This is what it looks like inside the engine:

(Airbus A380 FCOM - Engines - Thrust Reverser System)
The blue arrows indicate the flow of the so called bypass air, which is air that goes through the fan (and is therefore accelerated), but does not go into the core engine. With the thrust reverser deployed, this air is redirected forwards. The core air going through the actual turbine engine will still exit at the back.
Since there is more bypass air than core air1, there is a net thrust generated in the forwards direction.
If you are wondering what the pilots are doing to engage reverse thrust, this is a picture of the A320 family thrust levers:

(image source)
The main thrust levers are pulled all the way back during the flare to the position shown in the image (labelled 0). To open the reverser doors, you pull up on the smaller handles at the front of the thrust levers. Once the reverser doors have opened, the thrust levers can be pulled backwards to add more reverse thrust (range labelled REV in image). To close the reverser doors, the thrust levers are moved back forwards and the smaller handles are pushed back down.
Note that on a dry runway reverse thrust does not slow the aircraft down faster (assuming auto brakes are used). The brakes on the main landing gear are capable of achieving the same deceleration without reverse thrust. Engaging reverse thrust therefore reduces brake temperatures and wear.
The thrust reverser doors can look different depending on the engine type. Based on your image, the aircraft you were on was equipped with IAE V2500 engines2. The reverser doors on the CFM56 engine, as used on some A320 family aircraft, look a bit different3:

(image source: Wikimedia)

1 The IAE V2522-A5 engines used on the Airbus A319 have a bypass ratio of 4.9 : 1 (source).
2 FlightAware shows a EWG4063 flight tonight from Munich to Dortmund and according to planespotters.net Eurowings uses IAE engines on their A319s.
3 The CFM56 engine is also used on the 737, but uses the cascade thrust reversers there (thanks to DeepSpace for pointing this out). See also Why is the CFM56 produced with two different thrust reverse options?

Warning: Do not engage reverse thrust just after rotation on takeoff ! :-(. | Long ago an Air NZ in a training situation had one engine shut down on takeoff to simulate engine failure, unexpected by the pilot in control. Unfortunately the lever was able to be inadvertently pushed through the gate and into reverse thrust, resulting in loss of aircraft and AFAIR 2 killed, 3 injured. 1966. Numerous photos

The last paragraph about the CFM56 is a bit misleading. The CFM56 variants that are installed on the 737 (-3, -7) use the cascade thrust reversers. Only those that are installed on Airbuses (-5) have the pivoting-doors thrust reversers.

@DeepSpace Thanks, I updated the answer.

You say that thrust-reversers don't make you stop any faster.  That makes little sense to me.  From a quick search on this site, perhaps you're mixing it with the fact(?) that aircraft evaluation of landing distances is based on brakes only, not considering the help of thrust reversers.  Would more throttle when using reverse thrust reduce stopping distance?.  But that answer suggests that reversers + brakes could shorten total distance, which makes physics sense unless applying reversers somehow limits braking force at the wheels.

@PeterCordes I think they're saying that reverse thrust could make the plane stop faster but is actually mostly just used to reduce the amount of braking required to stop in the same time as if no reverse thrust was used

@PeterCordes No, I'm not mixing anything up. Note that I said "assuming auto brakes are used" (and auto brakes are almost always used on airliners that have them). The auto brakes always target a certain total deceleration. When adding more reverse thrust, the auto brake system will just use less wheel brakes to achieve the same total deceleration. Only on a slippery surface, where the anti-skid reduces wheel braking, will reverse thrust actually reduce stopping distance.

@Bianfable: thanks, I think I stopped skimming / reading at the surprising fact without even getting to the end of the sentence which would have answered my question >.<  My bad.  It makes sense that they're used in practice to take load off the brakes for a given target deceleration, I wasn't objecting to that.

It's the reverse thrust door opening. I will get back to you with a picture.

Courtesy By Pieter van Marion from Netherlands - PH-BVC KLM, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=29588152
For a brief explanation, once the aircraft has touched down (and in some cases even before it touches down) there are a set of doors and vanes which deflect the jet efflux forward which are deployed to help slow the airplane. However, these are generally NOT taken into account when certifying the airplane's landing distance. They are therefore a bonus when landing. There are two main types, Cascade vanes and  Clamshell doors aka Buckets. The A319 has cascade vanes, similar to seen in the image.
Some more trivia, the reverse thrust on some airplanes can only be activated when the nosewheel is on the ground, due to the possibility of the buckets scraping the runway with a high nose-up attitude.

The cascade reversers on the CRJ-200 were operated by a screwjack and flex drive cable deal and were really slow to extend.  By the time you had max reverse, a second later you got the speed call and it was time to go back to idle.

Apply reverse thrust before touchdown...?

@Jpe61 Yes, the Trident was an example.

Wow, something new every day, thanks!

@Jpe61 -- it's not seen on newer types, but the DC-8 made extensive use of in-flight reversing to make up for its lack of proper speedbrakes.  (In-flight reverse might be a thing on newer military transports, but I don't have the documentation to say that for sure)

At least some 4 engine miltary transports do use it for short field operations.

@UnrecognizedFallingObject - sure, why not? What could possibly go wrong?

@BobJarvis-ReinstateMonica -- there's some fairly complicated aerodynamics that determines whether in-flight reversing is safe or not (basically, it boils down to how badly reverse thrust messes up airflow over the wing -- DC-8s only use idle reverse on the inboards while in flight, for instance, that generates all the sink they need)

authors: Bob Jarvis - Слава Україні


text:
Can you log both XC PIC time and simulated instrument time together?
Are you permitted to log both XC PIC time as well as simulated instrument time (during the voyage over) whilst with a qualified safety pilot? I am pursuing my IR and would like to know if doing this is a useful strategy to build some hours in both required categories.
(I realize both pilots cannot log PIC XC time. Only one pilot can perform the necessary landing 50+ nm from the origin airfield in order to get the time there.)

Yes. As well as PIC: SEL, Day VFR.

I added the faa-regulations tag, if you're asking about another country then please re place it with an appropriate tag for that country. When you ask about regulations, please always tell us which country you're asking about.

You can log XC, PIC, simulated instrument, category/class, day/night, Total flight time.
From a regulation standpoint.
Cross time can be logged pursuant to §61.1

Cross-country time means -
Except as provided in paragraphs (ii) through (vi) of this definition, time acquired during flight -

(A) Conducted by a person who holds a pilot certificate;
(B) Conducted in an aircraft;
(C) That includes a landing at a point other than the point of departure; and
(D) That involves the use of dead reckoning, pilotage, electronic navigation aids, radio aids, or other navigation systems to navigate to the landing point.

For the purpose of meeting the aeronautical experience requirements (except for a rotorcraft category rating), for a private pilot certificate (except for a powered parachute category rating), a commercial pilot certificate, or an instrument rating, or for the purpose of exercising recreational pilot privileges (except in a rotorcraft) under § 61.101 (c), time acquired during a flight -

(A) Conducted in an appropriate aircraft;
(B) That includes a point of landing that was at least a straight-line distance of more than 50 nautical miles from the original point of departure; and
(C) That involves the use of dead reckoning, pilotage, electronic navigation aids, radio aids, or other navigation systems to navigate to the landing point.

PIC time can be logged pursuant to §61.51(e)

(e) Logging pilot-in-command flight time.

(1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-

(i) Except when logging flight time under § 61.159(c), when the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;

All others are logged as a requirement under §61.51(b)

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Why does the LEAP 1A HPT run at such a high RPM?
I've watched the N2 on the LEAP sit at 100% at cruise and fluctuate as high as 101%.  Why does the HPT run at such a high RPM?

If it helps, the EASA Type Cert shows that the max N2 RPM is High pressure rotor (N2): 19391 (116.5 % - 100 % N2 is defined as 16645 rpm)

What were you expecting it to be?  What other engine is your basis for comparison?  I'd say 100% N2 is fairly reasonable for cruise for modern GE cores.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What are these shaded areas?
What are these shaded areas? I looked in the Jeppesen legend, but couldn't find the answer. Thanks

It means that no Procedure Turn is required/expected if arriving within the sector defined by the 297 and 020 radials (inclusive) of DBL. The grey bars are a way of denoting the boundaries of the No PT sector (the entire pie section between the radials) without obstructing too much of the other details. That's why the bars are bordered on the north side of the two airways.
The Jepps wording seems to generate quite a lot of confusion because of the practice of including the words "Via Airway".  I found a message thread here that might help a bit.  Just remember that if confronted with something like this on a check ride and are confused, express your confusion to ATC and ask for clarification rather than blunder into a wrong move.


text:
Is the procedure turn mandatory at non towered airports?

Here is instrument VOR-A approach at Eagle Lake. If I am coming from the north, it looks to me a big waste to make a procedure turn. On the other hand there is nobody there to approve straight-in approach like in controlled airspace. Any good explanation why I should or should not to make this PT?

You're still controlled by Approach, right?

nop, it's Golf airspace

@Roman Mandeleil, as I establish in my answer below, the approach is in controlled airspace.

The question is flawed because it presumes that you are flying a published instrument approach procedure in uncontrolled airspace without an IFR clearance.
Looking at the VFR sectional you can see that there is a shaded magenta border around this airport that signifies Class E airspace, (controlled airspace) with a floor of 700' above the surface.  You cannot fly in controlled airspace, in IMC, without an IFR clearance.  And the published procedure contains a couple hard altitudes well above the 700' floor.

The reason for this is to control and protect instrument traffic going into and out of uncontrolled airports during instrument meteorological conditions.  In order to get into the Class G airspace from the surface to 700' above the field during IMC, you need to first transition through the overlying Class E.  The published altitudes for the procedure turn are in controlled airspace, and the square "keyhole" extension to the North would seem to exist for the very purpose of containing this procedure turn.
So in short, you fly what you are cleared for.  If cleared for the straight in approach you would not have to execute the procedure turn.  The presence or operation of a control tower at the field is not pertinent to the question - tower doesn’t clear you to fly an instrument procedure, the approach controller does.
Worth noting, if cleared for a straight in RW 17 approach with weather at minimums, you would only be in Class G, (uncontrolled) in IMC for about 200' or roughly 20 seconds descending before you would either break out and continue in VMC, or go missed.  Not a lot of exposure, or freedom for creative deviation...

Thanks for the details . . . not having done too much of this, my quandary would be how to transition from the 2,100ft MSA to 1,400 FAF altitude at the VOR?

If you are coming from the North and request the straight in, ATC would probably clear you down to 1400’.  And if they didn’t, just ask for it.

If ATC is able to clear me, I have no issues. I meant otherwise . . in IMC no surveillance radar avlbl that day?

I do know that sometimes the FAF may be approached at a nominal 3deg vertical flight path reaching 1400ft at theFAF.

@skipper44, I am not familiar with ATC’s minimum equipment requirements for providing IFR separation, but if they are unable to clear you then you are unable to fly it.

@skipper44, you would not transition from the MSA. The MSA is for emergency reference only. You would get an altitude assignment from ATC. ATC probably doesn't have radar service there and that low, but radar is not the only way ATC keeps track of aircraft. On approaches like this, only one aircraft will be cleared for the approach at a time, and they will not clear another aircraft in or out of that airport until you've called in that you're on the ground or missed the approach.

@MichaelHall -- re comment "as I establish in my answer below, the approach is in controlled airspace. " and answer "it presumes that you are flying a published instrument approach procedure in uncontrolled airspace without an IFR clearance." -- is your assertion that the entire published instrument approach procedure is in controlled airspace?  Wouldn't the published "approach" also be considered to encompass the distance beyond the final approach fix, on to wherever the aircraft breaks out IMC?  I'm just asking because while you are undoubtedly right that the pilot is not free to invent

@MichaelHall -- (ctd) not free to invent his own approach in controlled airspace, the answer seems to imply that there no such thing as legally flying on an instrument approach in IMC in uncontrolled airspace.  Which I don't see how can be justified.  It seems to me that many published approaches are partly in uncontrolled airspace.  Maybe it is just a matter of terminology but I don't see how the term "approach" would only apply to the portion in controlled airspace.

@quiet flyer, I thought I made it clear that only 200  vertical feet on the straight in was in G, but I am open to any suggestions to clarify this...


text:
How often do pilots fly drunk?

AVweb reported: 2018.07.30 - A former pilot for Alaska Airlines was sentenced on
  Wednesday to a year and a day in federal prison, for flying two
  flights in 2014 with a blood alcohol level more than three times the
  legal limit.
Arnston flew from San Diego to Portland on June 20, 2014, and then
  from Portland to John Wayne Airport, in Orange County. After landing,
  Arnston was selected for random drug and alcohol testing by airline
  personnel. Two breathalyzer tests showed Arnston had a blood alcohol
  concentration of 0.135 percent and 0.142 percent. The federal limit is
  0.04.
BoardingArea reports: 2018.09.02
  Prosecutors allege he struggled with alcohol addiction over those two
  decades and routinely piloted commercial flights under the influence
  of alcohol.

Are there any published statistics on the percentage of pilots tested or otherwise gleamed for alcohol that failed?
How often do pilots fly drunk?

Youtube 1
Youtube 2
Youtube 3
Fox News

Not more than once in their career.

@GregHewgill I appreciate your statement as humor, but, just to be clear and in case someone might think it would happen only once in their career, my observation has been that while it may be rare that pilots fly drunk, it is even rarer that they get caught. See the 2nd to the last paragraph of http://terryliittschwager.com/Journal/1998-05-23_1998-12-16_none.html for an instance of a competent pilot getting caught accidentally. I flew with him regularly, and never observed anything but good performance even though I suspect he might have had trouble with a breathalyzer test.

@Terry: Thanks, and you're right that my statement is meant only as humor. Though, in today's environment, I suppose pilots would only get caught once drinking and flying.

Are you asking about commercial pilots or pilots in general? I've heard hangar stories (one involving a pilot who could barely stand as they refilled the 172 at a self serve, then took off with twin trails of fuel mist because they forgot to put the caps back on), but other than the occasional news story I've never heard of a GA pilot getting caught for this (at least not unless they were referred to as the "accident pilot").

most pilots never fly drunk. The rest don't do so often enough that it causes serious problems, in fact do so so rarely that when they do get caught it's major news.

Drunk, under the influence of alcohol, or "unable to pass an alcohol test"? Because that make quite a huge difference...

...more than three times the legal limit... there is a legal limit?? seems .. federal limit is 0.04 I  really though it is 0.0

@gusto2 there are some interesting problems with setting a 0.00000 limit, even if you assume perfect measuring hardware: undeclared trace quantities in foods (desserts, wine in sauce, ripe fruit); some people take much longer than others to remove alcohol, leaving traces for a long time; byproducts of ketogenic diets

Its rare but it does happen. You can search the NTSB database here, the phrase "positive for alcohol" yields the best results as toxicology is fairly common in an accident so a lot of reports include "negative for alcohol" making "alcohol" alone a bad search term. I was able to find a few examples here, here, here, and here as well as some more report results.
according to this article

... Of over 10,000 pilots randomly tested for alcohol in 2010, only 12
  failed the test.

They don't cite any sources though.
This looks like it might be the original study and has slightly different numbers but this seems to include all "Aviation Employees" so pilots, crew, ATC and the related may have been included.

Validity of Suspected Alcohol and Drug Violations in Aviation Employees
Results:
  During the 11-year study period, a total of 2,284 alcohol tests and
  2,015 drug tests were performed under the reasonable-cause testing
  program. The PPV was 37.7% [95% confidence interval (CI), 35.7–39.7%]
  for suspected alcohol violations and 12.6% (95% CI, 11.2–14.1%) for
  suspected drug violations. Random testing revealed an overall
  prevalence of 0.09% (601/649,796) for alcohol violations and 0.6%
  (7,211/1,130,922) for drug violations. The LR+ was 653.6 (95% CI,
  581.7–734.3) for suspected alcohol violations and 22.5 (95% CI, 19.6–25.7) for suspected drug violations.

The FAA also has an interesting fact sheet you can find here quoting some accident numbers from the late 80's and early 90's as well as the pilots BAC.
Its worth noting that the regulations have changed a fair bit over the years. The current regulation for this is FAR 91.17 which establishes an 8 hour "bottle to throttle" time frame as well as a maximum .04 BAC.

§ 91.17 Alcohol or drugs.
(1) Within 8 hours after the consumption of any alcoholic beverage;
(2) While under the influence of alcohol;
(3) While using any drug that affects the person's faculties in any
  way contrary to safety; or
(4) While having an alcohol concentration of 0.04 or greater in a
  blood or breath specimen. Alcohol concentration means grams of alcohol
  per deciliter of blood or grams of alcohol per 210 liters of breath.

If you take a look at the original amendment creating 91.17 it reads

Sec. 91.17 Liquor and drugs.
  (a) No person may act as a crewmember of a civil aircraft -
(1) Within 8 hours after the consumption of any alcoholic beverage;
(2) While under the influence of alcohol; or
(3) While using any drug that affects his or her faculties in any way contrary to safety.

the important difference being that it does not establish a maximum BAC but leaves it open to the interpretation of "under the influence" which potentially left room for intoxicated pilots prior to the current verbiage.

This seems pretty accurate. In the 70-80's I would say 1/15-20 of my pilot friends flew drunk (over 0.1). At the time, I was told the 60-70's were probably 1/5-10. By 2000, I knew less other pilots but got the impression none were drinking on the job. Your stats show it is now about 1/1000 which seems reasonable. In the 70-80's the law simply said you could not consume alcohol within 8hrs of flying, most didn't but that didn't keep them from being hung over. If there are 5000 airline flights in the US per day, and many are multiple puddle jumps, perhaps 20-30 pilots are drunk each day.

@jwzumwalt  Taking a guestimate rate for all pilots, including GA pilots with no crew, no passenger or supervisory interactions and virtually no program for random or "for cause" testing, and extrapolating that out to airline flying gives you a result that is WILDLY inaccurate. Five thousand flights per day in the U.S. is low by a factor of several, and "20-30" is almost certainly high by a similar factor. I won't suggest that the rate is uniformly 0.0, but there is NO WAY 20 airline pilots are flying drunk & unnoticed each day. Nobody tolerates that these days in airline flying. NOBODY.

Also note that (4) counts people having alcohol levels due to other reasons than drinking as illegal to fly. Some medical conditions can cause this to happen (though it's quite likely that such people would fail their medical, you'd have to consult an AME for that).

There may also be a number of cases where alcohol contributed to a fatal accident, but we won't know because alcohol testing is not done on deceased pilots

@TomMcW im not sure if you are referencing unrecovered bodies but Toxicology including alcohol testing is routinely done on deceased pilots. some of the reports I have linked are good examples of such testing.

The NTSB does not generally include alcohol in the tox reports because it's highly unreliable after death. Decomposition creates a fairly substantial amount of ethanol and from what I understand it can be inaccurate within minutes of death.

If I have time later I'll see if I can find a citation for that, but I've read it before in regards to NTSB investigations

@TomMcW I also came across that in my research but it appears they note it in the report as "alcohol content could not be determined due to natural alcohol as a result of decomposition" (or something like that) but I only found this on some of the reports I came across. The ones I have linked seem to be conclusive in their results.

Thankfully this really does not happen all that much, most airlines have processes in place to catch those with a problem and there are programs available. This is because drink is recognized as a sickness and therefore treatable.
We have also seen willingness on the part of ground staff to report any unusual behavior and there have been several cases where the pilot has been prevented from flying.
A drinking problem usually becomes apparent in unusual behavior long before the stumbling appears. Typical pointers..
1. Punctuality issues.
2. Poor personal hygiene, sloppy dress.
3. Car has numerous dents.
4. Proceeds direct to aircraft instead of report to the despatch office (using lateness as an excuse).
5. Addiction to breath mints.
6. Irrational outburst/ bad temper / mood swings.
Each in its own is not an indicator but when a few are present then its time to look deeper. Sad to say its usually the first-officers who notice this first and this is where good a healthy reporting culture is required to allow them to speak up.
Another pointer is when someone leaves a bigger airline in favour of a smaller airline .. while a lot of pilots really want a change of pace, a wise fleet manager will have a quite word with his ex-employer.

"...a wise fleet manager will have a quite word with his ex-employer." In the US, it is against the law for employee information to be exchanged without the employee's explicit permission. Further more, most HR departments won't do it for litigation, if there were an accident, i.e. "why didn't they handle a safety risk...". Without employee permission, there are only two questions that may be asked, the more serious is, "Would you re-hire this employee?". HR is only allowed a yes/no. It has become nearly impossible to get reliable past employee information.


text:
Has a micro-burst or wind shear caused fatalities on takeoff?
Delta Flight 191 at Dallas-Fort Worth (1985), TANS Perú Flight 204 in Peru (2005), FedEx Express Flight 80 in Japan (2009), and Eastern Air Lines Flight 66 at New York's JFK, are all examples of aircraft fatalities due to wind shear or micro-bursts during approach.
Have there been any airliner fatalities due to micro-bursts or wind shear on takeoff?
 source
UPDATE: As a hobby, I have spent my life following aircraft accidents. At the outset of this question, I was unaware and doubted any such occurrences had happened. The answers have certainly been an eye opener and shows the breath of knowledge this group has.
So far:
Canadair C-4 Argonaut three crew and 29 passengers killed
Pan Am Flight 759 all 145 on board and 8 on the ground killed
Spantax CV-990 crash of EC-BNM off Arlanda (1970)
Continental Flight 426, Denver, (1975)
Continental Flight 63, Tucson, (1977)
United Flight 663, Denver, (1984)
(possibly - AeroméxicoFlight 2431) (2018)

The first example in the Wikipedia article on microbursts states "...crash occurred ... when a ... four-engined Canadair C-4 Argonaut airliner ... crashed into a tree on departure ... three crew and 29 passengers were killed".   The fourth example is "Pan Am Flight 759 ... crashed ... after being forced down by a microburst shortly after takeoff. All 145 on board and 8 people on the ground were killed."

Does the 1970 Spantax CV-990 crash of EC-BNM off Arlanda count?

Probably a bit early to be sure, but it seems yesterday's Aeroméxico Connect Flight 2431 suffered this issue on take-off.

I had the same thought... interesting.

Have you done any research at the NTSB Aviation Accident database?  https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx

AeroMexico might have just made an entry to the list.

One (of several) incidents that I remember was Pan Am Flight 759. It encountered windshear after takeoff from New Orleans' Moisant Airport July 9, 1982 and crashed, killing all aboard and several on the ground.

"One (of several) incidents"... what others are there?

Cursory googling results in a report by University of Chicago’s Dr. Ted Fujita and Dr. Horace Byers discussing the matter.  Takeoff related incidents from that: Continental Airlines Flight 426, Denver, 1975; Continental Airlines Flight 63, Tucson, 1977; United Airlines Flight 663, Denver, 1984.


text:
Why do narrowbodies have longer life than widebodies?
Is it fair to say that narrowbody aircraft have a longer life than widebody aircraft? This is the conclusion drawn from a report written by Dick Forsburg from Avolon (.pdf), where he says that the average life of a narrowbody is 26.6 years, while the average life of a widebody is 24.6.
Is it generally accepted that narrowbodies have a longer life than widebodies? If so, what are the reasons for narrowbodies having a longer life that widebodies?

A few dozen DC3s are probably skewing the statistics.

What happens when you design a structure with a very new technology, using slide rules, with a relatively crude understanding of fatigue, so you add oodles of margin, and end up with an airplane with a near infinite fatigue life.  As a product that, still to this day, businesses still purchase to put to work and make money over 85 YEARS after it was designed, the 3 is the greatest engineered conveyance of the 20th century in my book.

This question is ambiguous. The reference discusses economic life and has the data you quote, rendering any other answer moot. You do not specify economic life, which makes me wonder whether you actually mean design life (how long the aircraft is intended to last) or maybe cycle life (which type is built more durably)

The author does a very good job explaining the jet market. The key take-away is that it's all about economics. In many ways, narrowbodies may "wear out" faster as they typically fly shorter routes and accumulate more cycles in a shorter period of time. Pressurization cycles are a big factor in structural fatigue.
But that's not the primary reason for retirements. Airplanes get retired when operating them is no longer profitable. Profit is generically income minus  costs. Income for aircraft is maximized by flying as much as possible (high utilization) with the highest load factors possible. Costs are primarily driven by capital depreciation, fuel, crew, and maintenance.
The shorter lifespan he identified for widebodies is driven by a few key factors:

Widebodies are a smaller percentage of the total fleet, so that even
a few "early" retirements will cause a larger shift in the average.
Widebodies are suited primarily for long-haul, high density routes.
So a shift in travel patterns can quickly leave a route
unprofitable. Covering that reduced demand will often mean shifting
to a smaller aircraft to keep the load factors up. Narrowbodies have
more inherent flexibility.
And what I would say is one of the most significant factors is the
shift of widebodies from 4 engines to 2 engines over the last 20-25
years. It's not a fast process as widebody construction is not very
high rate, but the cost benefit of 2 engine widebodies (B777, A330,
A350) means a lot of 4 engine aircraft (B747, A340) have been
retired in the last 10-15 years.

I would guess that there's also probably less third-world secondary market willing to buy really old aircraft in the case of wide-bodies compared to narrow-bodies.

The article says that narrowbody aircraft have a longer lifespan than widebody (26.6 years vs 24.6 years). So pressurization cycles may not be a determining factor.

@zundi Edit answer to clarify that structural issues aren't a primary reason why airplanes get retired.

Zundi is right - short-haul aircraft accumulate their cycles in much less time, so a longer lifetime means that many more cycles are accumulated. However, short-haul aircraft are also designed for more cycles (guess why!), so the overall conclusion is not valid. What is more significant is that very old aircraft will dominate the statistics - wide bodies are simply not long enough around!

So how many cycles is a heavy designed for?  40 or 50k?

A previous post said the 737-400 design airframe life is 75000 cycles.  The RJs have a design life of 80k.  Not a big difference.  But I would be interested to see if really long haul aircraft have a much lower design life, like say 50k.

@JohnK The 747D intended for domestic use in Japan had a design cycle life of 50,000 compared to 24,600 for a standard one. Both of these numbers would be higher for current short and long haul aircraft, but the 2x factor still holds.

The author has a masters degree in marketing, so please do not expect an expert in statistics. Adding up some numbers without correcting for effects will lead to wrong conclusions. When almost all 707s and DC-8s are retired already but one quarter of all DC-10s and half of all A300s are still in service, it is simply too early to give an "average" retirement age for wide bodies.
It would be better to only compare aircraft from a specific time period, like the 1980s, but to simply add all up will produce misleading results since wide bodies are not around long enough and have been introduced with high-bypass fan engines already, so they can still be operated profitably, if only as freighters.

As stated in the comment above, if you mean economic life the reference you quote already proves the answer in the current environment.
The reason narrowbodies are currently kept in service longer than widebodies is due to the extraordinary demand for narrowbodies due to extreme growth of LCCs and competitors following a period of world wide deregulation. If you can't get a new aircraft you keep using the old one, even if it is not as efficient as some newer unavailable model. This environment may change at some point, and the answer will change with it.
If you mean design life, commercial aircraft are typically designed to last 30 years though this has been lower in the past. A narrowbody's life is much tougher than a widebody's so they are built tougher; they have a higher cycle capacity built into them.
A typical widebody would wear out rapidly if exposed to typical narrowbody usage. If you look at the 747D made for JAL/ANA to use on domestic routes, it not only was packed with a larger than normal number of seats, increased gross wt and reduced fuel capacity, it was also reinforced to endure the additional wear. Its design cycle life was 52,000 compared to a standard 747 at 24,000. It also had derated engines to lengthen their useful life.

The cycle length is the biggest factor I think.  Airframes are generally designed to be economical to operate to 80000 cycles, but often the airframes start to require patching and reinforcement of the structure at around 40-50000 cycles to avoid increasingly onerous inspection requirements.  Airframes get retired when the cost of incorporating the structural reinforcements exceeds the benefit.  Regional Jet aircraft that do a cycle every 1.2 hours suffer the most from this and many get retired after only 20 years of service because it's not worth patching them up.  In general, the longer the average cycle time, the more years that can be squeezed out of an airframe.

If I'm not mistaken, you are actually explaining the opposite: why smaller aircraft should be retired earlier, when the OP is asking why larger ones are.

Good point lol. My expertise is in the regional world.  People would complain about how RJs were being retired so early from an hours standpoint and I would point out that a 767 with 40000 hours has less than half the cycles of a regional jet.

The article says that narrowbody aircraft have a longer lifespan than widebody (26.6 years vs 24.6 years).

Your cycle count is only correct for short-haul aircraft. Long range design cycles are maybe half as many.

Well yes of course an airplane averaging 4 hour legs will have not much more than a quarter of the cycles of an RJ for the same flight hours.


text:
What happens during Engine Performance Restoration
What is the typical process during an Engine Performance Restoration?
I am trying to find a resource that gives an overview of what happens but I have not been successful.
Any help would be much appreciated.

This isn't very clear @TomLynch, what kind of engine and who is offering the service?

An engine performance restoration is a scope of work ("workscope") for a turbofan engine shop visit, where the engine is removed from the aircraft and sent to a engine maintenance facility and the engine case is opened.
An engine performance restoration involves the inspection, rebalancing or replacement of specified parts in the core gas flow path, that is, HPC, combustor, and HPT. These parts are most critical for the fuel burn and EGT margin of the engine. If any of these parts are life-limited, they will be changed at this point.
It also should include any mandatory inspections or replacements, covering the whole engine, dictated by the manufacturer or regulators.
It excludes any optional refurbishment or inspection of the fan, LPC, LPT, and gearbox. It may also exclude inspection of parts deemed non-performance critical in the core.
Because of this, the cost of the visit is reduced, but the engine will not be as efficient and potentially require another visit sooner than a "full overhaul". Thus, an engine performance restoration is the most basic scheduled engine shop visit. It is common that a performance restoration be alternated with a full overhaul.
See Engine Maintenance Concepts or Basics of Aircraft Maintenance Reserve Development and Management for a more detailed overview.


text:
How can I calculate the Obstacle Free Zone of an aerodrome?
How can I calculate the Obstacle Free Zone of an aerodrome?

AS per ICAO Annex 14, Obstacle free zone (OFZ). The airspace above the inner approach surface, inner transitional surfaces, and balked landing surface and that portion of the strip bounded by these surfaces, which is not penetrated by any fixed obstacle other than a low-mass and frangibly mounted one required for air navigation purposes.
For easiness it is a rectangular area around the runway which extends 60M for Code 4E runway and 77.5M for Code 4F runway from runway centre line sideways and 60M from the runway thresholds.


text:
Chemtrail Conspiracy theory
Could this be true?  https://www.facebook.com/migyal.imisyou/videos/2514422715448542/UzpfSTEwMDAwODE2OTc1NjA4NDoyMDQxMDc4Nzg2MTc0NDI3/    A friend has posted this - of course, I have been looking around to debunk it, maybe someone can give me an answer.  thanks in advance.

Maybe you could include the relevant elements of the video in the question.

You may first search for yourself and be more specific about why you think "this" is true or not. Remember not all aviation.SE users have a facebook account so you must explain what your link is about.

This sort of question is a better fit for skeptics.SE, but please note that they only address notable claims, which may not include a random Facebook post

The fact that this even needs to be debunked is ridiculous. I have worked on both military and civilian aircraft of many, many different varieties. I have never once been called to a jet with a malfunctioning “Chemtrail” system. I have never seen a maintenance manual reference for it, never been trained on it, and have never even seen provisions for such a system that might be worked by some sort of “covert contractor.” It is either the aircraft system that all other aircraft systems should emulate, or it simply doesn’t exist.
This is perhaps the dumbest conspiracy theory ever and simply feeds on people’s innocent yet ignorant understanding of aviation. No. It is not a thing. It’s not even close to a thing.

The title is misleading, the video try to say that fuel cannot fit in an aircraft, cannot be pumped fast enough, and use poor photoshop to "prove" this.

Still aircraft carry "extinction" probes used for scientific experiments on clouds (source), you can't say the contrary ;-)

For those who did not watch the video (btw, I have no FB account and will never have one):
It is a polemic about the fuel load aircraft can take. The author claims:

we have been deceived by a conspiracy of airlines and aircraft manufacturers about the amount of fuel that goes into an aircraft.
the mass of the claimed fuel volume is too heavy to be lifted by an aircraft.
the volume would not fit into the wings.
the filling process would not allow to pump the claimed volume in the given time.
fuel sloshing would be an insurmountable problem.

and so on. I stopped watching after half the video because the ruse had long become obvious.
I have done many calculations on how much energy is contained in the fuel and how much is needed to move an aircraft over large distances. If you read some of my answers on the subject, the results can be found even on this site. Now for a rebuttal:

FB is the premier platform for spreading fake information. Whoever still believes what is posted there must have been living under a rock for the last decade. So the source makes this already suspect.
The fuel needed for a given flight is only a fraction of the maximum fuel load. This maximum is only needed for extreme range and can reach up to 40% of the take-off weight. So there is clearly enough lift capacity for the structure, the systems and the payload. Fuel mass is an issue, but it is manageable.
The tanks are in the wings, but also in the horizontal tail and the center wing which is inside the fuselage. The tanks are not special canisters like in a car, but integral tanks: The structure is sealed and riveted tight so the whole inside can be filled with fuel. The available volume is used to the extreme, and yes, it is sufficient.
Filling is done with special, high-performance equipment. I found the part about the claimed impossibility of the filling process to be especially ridiculous.
Yes, sloshing is also a problem with aircraft tanks, but they include baffles and sometimes even a special foam to reduce sloshing.

My conclusion: This is yet another silly conspiracy theory and clickbait for people who don't know enough about aircraft engineering.

Regarding "the volume would not fit into the wings", there's my answer to How is fuel weight calculated? which (in response to a comment on that question) discusses that issue specifically. I personally found that result somewhat surprising; if an A380 used the entire wing area for fuel tanks, and nothing else (neither of which is the case in practice), then the tanks would need to be less than 40 cm high to contain the referenced amount of fuel.

@MichaelKjörling: Yes, and Antzi has done the same in his answer. I will link to to your answer.

Upvoted for "no FB."

Fuel capacity:
Funny how the video just insert non scaled fuel trucks next to the aircraft instead of... Doing the maths.
A380 wing area: 845m²
Fuel capacity: 253T <=> 320 000L <=> 320m³
So how high does your wing need to be to contain that much fuel ?
322m³/845m² = 0.38m = 38.1cm
Obviously this is an over simplification but the answer is yes, it fits.
Sloshing:
The tanks are divided to prevent that, research the site for more informations.

Sorry that I could give you only one upvote. Great response to that silly claim!

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What is a "polar front low" and what is its usual direction of movement?
As part of my learning to the meteorology exam for PPL I seen the following question -
"What is the usual direction of movement of a polar front low?"
the answer is - "Parallel to the warm-sector isobars"
the first problem here that I didn't found any information about what is a Polar front Low? is it the same as just Polar Low ? a polar air mass depression?
second problem, I didn't found any information about why the polar front low movement  is parallel to the warm-sector isobars... can someone please refer any relevant information?
I really tried to find the answer myself...

A polar front low is a low pressure system that's associated with the polar front. Polar front is the prevailing front (the red line in the picture) between the polar air cell and the Ferrell cell.

Sometimes a local disturbance in the polar front forms. How and why exactly these disturbances begin to form, is way above my education, but I don't think anyone else knows either (I read an article about that a few years ago, and basicly it said "nobody knows" spanned over 8 pages). There are several contributing factors, including the North Atlantic Oscillation, air pressures, winds etc.
Simplified though, "a dent" in the polar front forms and begins to rotate and move along the polar front. This local low pressure system is called the polar front low.
A cold and warm front form adjacent to the low pressure center. Both fronts have their own movement direction and speed, and they rotate around the low pressure center.

Source: http://www.eumetrain.org/satmanu/polar_front_theory/index.html
The whole system moves in the direction of the isobars in the warm sector, and with the speed of about 80% of the geostrophic scale measured between the first and second isobars in the warm sector (the red area in the third picture).

Thanks for the perfect answer!!!

Meteorology is a complicated subject. I'm glad if I was able to shed some light on the matter.


text:
How can I compute indicated altitude?
I would like to compute what an altimeter would display given a true altitude and atmospheric conditions.  Specifically:
Given:

True altitude, in feet
Outside air temperature, in degrees C
Local altimeter setting, in inHg (e.g. from nearest metar)
Kollsman setting, in inHg (which may or may not be set correctly to the nearest metar)

I would like to compute indicated altitude.  If it simplifies things, assume I only care about altitudes below FL300.
I've tried applying the formula from here in reverse:
$$A_I = \dfrac{1000 \cdot A_T}{4 \cdot \Delta_{ISA}+1000}$$
but I'm not sure if this accurately represents how altimeters work or if it is meant to be an approximation.  Also, it does not take into account the difference between Kollsman setting and local altimeter setting.

I suppose this question can be split into two separate parts:

A pressure altimeter takes as input the ambient pressure and Kollsman setting and outputs an altitude.  While this isn't done electronically (at least in the "steam gauge" type), what formula encapsulates what it is doing?
Given true altitude, local altimeter setting, and ambient temperature, what will be the ambient pressure?

To answer your question #1, you're right, altimeters take 2 things in input:

QNH, a.k.a. altimeter setting
Static pressure P coming from the pitot system

Altimeters assume that both the QNH and the air pressure are values within the International Standard Atmosphere (ISA). I'm not sure how this is carried out mechanically in the altimeter but this is the equation they solve:
$$h=\frac{T_0}{L}\left[\left(\frac{\mathrm{QNH}}{P_0}\right)^\frac{R_sL}{g}-\left(\frac{P}{P_0}\right)^\frac{R_sL}{g}\right]\tag{1}$$
where:

$h$: Altitude reading in meters
$P$: Air pressure in Pascal
$\mathrm{QNH}$: Altimeter setting in Pascal
$L$: Temperature lapse $=0.0065 \mathrm{~K/m}$
$T_0$: Standard temperature $=288.15 \mathrm{~K}$
$P_0$: Standard pressure $=101325 \mathrm{~Pa}$
$g$: Gravitational acceleration $\approx 9.81 \mathrm{~m/s}^2$
$R_s$: specific gas constant for dry air $\approx 287.058 \mathrm{~J \cdot kg^{−1}K^{−1}}$

To answer question #2 all we need to do is to invert equation 1:
$$P=P_0\left[\left(\frac{\mathrm{QNH}}{P_0}\right)^\frac{R_sL}{g}-\frac{Lh}{T_0}\right]\tag{2}$$
just be aware that in this case $h$ is not the true altitude, but the altitude indicated in the altimeter. If you want to use true altitude you first need to compute it, inverting the relation you also mention in your question:
$$h_{true} = h + \frac{4\cdot h}{1000}\cdot\left(T_\mathrm{OAT}-T_\mathrm{ISA}\right)\tag{3}$$


text:
How did the FAA decide that firewalls should resist fire for 15 minutes specifically?
I'm searching for information on where the criteria of 15 minutes come from, in which the firewall is subjected to by a flame of 2000 °F (according to the now-obsolete 14 CFR 23.1191).
I know that this time includes mainly a reaction time. This reaction time is the time from the appearance of a fire in a compartment to the fire being recognized by the pilot.
Can anybody provide more information about the 15 minutes?

Most likely a time considered to take from the start of the fire, noticing it, shutting off fuel, and burning off the fuel already delivered to engine, plus added safety margin of some minutes (30% maybe).

I suspect that this criteria is part of the rules which are not "computed" but rather decided based on experience and various non-analytical considerations.

You might be able to dig it out of the federal register. It might also be a carryover from the CAB rules that precede the regulations in CFR Title 14.

It's possibly carried over from railroad requirements.  One of the weirdest things I've learned in studying the 7110 is that our time/distance rules  (10 minutes/20 miles) came out of railroad timetable requirements that were initially set forth in the 1800s.


text:
How accurately do I need to maintain my altitude while VFR-on-top?
Is holding altitude as stringent a requirement when flying VFR-on-top? If the deviation exceeds say 200 feet off a given VFR altitude (i.e. 5500’ heading eastbound) is this as big of an issue for ATC?

Am I right to assume you're receiving a service from ATC, either ATSOCAS or you're in CAS?

Considering, as a pilot, you should be able to maintain an altitude with Less than a 100 foot accuracy, I would say that you should be doing the same when VFR-on-Top. If you change (vacate) that altitude for any reason, you should let ATC know. They are still maintaining aircraft separation. They need to anticipate your current and future position. If it’s a brief departure from the previously reported altitude (say for instance, due to turbulence), reporting the discrepancy is not important if you return to the original altitude immediately. Though, you might want to give ATC and/or FSS a PIREP.

In the US, when I enter "OTP" in your flight plan, my radar will display your reported mode C altitude. If you're consistently out of tolerance (200 ft) from a VFR cruising level, and I've given you a current altimeter, it's my job to advise you of the discrepancy.
After all, your equipment could have a problem.
If you reply that you're having trouble holding altitude for weather, or staying clear of clouds, and I have no traffic for you, I'll probably leave it be for awhile, but I will check up on you.
There are also times when I may use the phraseology "VFR cruising levels for your direction of flight are (odd/even) cardinal altitudes plus 500 feet". This is usually in conjunction with traffic advisories, such as, you're flying eastbound at FL105, but I've got westbound traffic at the same altitude, that may be in conflict. They're at a correct cruising altitude, so I'd give you the advisory.

See AIM 5-5-13. The clearance must be requested in the flight plan or subsequently. 5-5-13(a)(1) and AIM 4-4-8. There are 3 requirements: 1) The pilot must fly at an appropriate VFR altitude as defined in 14CFR91.159, comply with VFR visibility and cloud clearance as established in 14CFE91.155 and finally, comply with the IFR rules applicable to the flight. By requesting VFR on Top, the pilot assumes see and avoid responsibility and, per 5-5-13 (a)(3) should advise ATC of any altitude change prior to making such change. Typically ATC will approve VFR on top if the clearance is requested but the pilot continues to be controlled by his IFR flight plan and remains clear of Class A airspace.  PIREP’s as to top heights and layer conditions assist ATC in the assignment of such a clearance and flight level.


text:
Can another pilot act as my safety pilot for only part of a flight?
Let's say I fly with my safety pilot while under IFR plan (I recently earned my IR). I cancel IFR in air since I can maintain VFR for the last, say, 20nm of the journey (assume there was just some weather necessitating the rating earlier on enroute).
In the VFR phase, I don my hood and conduct 1 or 2 practice instrument approaches at or near destination.
First of all, is this ok? Passenger (since right seat sits VFR only pilot) "evolves" into safety pilot?
Second, if legal, how would one log this flight for purposes of currency?

I added the FAA regulations tag because it seems likely that you're asking about US regulations. Please always tell us which country or regulations you're asking about. If you aren't asking about the US, you can just edit your question to add the correct information.

Yes. This is all perfectly in accordance with the regulations.
You personally conducted the IFR flying through IMC, as an instrument rated pilot on a filed IFR flight plan. Check.
You cancelled the IFR flight plan midflight with a plan to continue VFR. Check.
In VMC, your VFR-rated pilot friend assumes the responsibility of acting as safety pilot while you undertake practice IFR approaches in simulated IFR. Check.
When logging the time, you would log the total time as PIC for yourself. Your friend was acting as a necessary crew member, but NOT necessarily as PIC. Nevertheless, his name and certificate number should be logged in your book as well. You would record the portion of your flight that was through IMC as ‘actual IFR time’ and your time under the hood as ‘simulated IFR time’. You would record your practice approaches and count them toward your required six-in-six as long as they were performed according to the required standards.
I found this article at Pilot Workshops that can provide you with more detail.
Clear skies!

For completeness, the VFR-only friend would log SIC time for the portion of the flight where he was a safety pilot. He was a passenger for the rest of the flight; he couldn’t have been acting as PIC due to the IFR segment.

@StephenS That's one option although the OP said that they cancelled IFR and the safety pilot acted as safety pilot only under VFR. In that case, they could have agreed that the safety pilot would also become the acting PIC, allowing both pilots to log PIC time. Assuming the safety pilot was qualified to act as PIC of the aircraft, of course.

The safety-pilot certificate number is not required by the FAA. "§61.51   Pilot logbooks. (b) (v) The name of a safety pilot, if required by §91.109 of this chapter."

@Pondlife I’ve always assumed APIC was fixed for an entire flight. Is there any source saying it isn’t?

@JScarry: I only suggest recording the certificate number for convenience of reference in the case of an audit. It is not strictly required, as you say.

@StephenS: There is nothing preventing one properly qualified pilot from handing off PIC responsibility to another qualified pilot midflight. This link explains your question, among other details: http://www.naplesflyingclub.com/SafetyCorner/PIlot%20In%20Command%20-%20Acting%20vs%20Logging.pdf

@Pondlife: As I understand it, you are correct. At least, that is the interpretation that I’ve always been told. That said, if at ANY TIME his safety pilot must touch the controls to maintain safety of the aircraft, the pilot under the hood loses his “sole manipulator of the controls” caveat.

@StephenS See the definition of PIC in 14 CFR 1.1 (emphasis mine): "Has been designated as pilot in command before or during the flight; "

@AaronHolmes Yes, that's my understanding too. We have quite a few questions on this site about logging time with a safety pilot in various combinations of VFR/IFR and VMC/IMC and who can log what.

First, congratulations on getting your IR!
On the assumption that you already know the requirements for having a safety pilot while you are under the hood, why would it be any different than if you took off under VFR?
I think you are overthinking this.  The fact that the first half of the flight was under IFR is largely irrelevant.  Your co-pilot is either an appropriately rated safety pilot, or not.  They don't start out as a mere "passenger" and then "evolve" into something else depending on the rules you are operating under.
And you should log it the same way you would performing any practice approach under simulated IFR.  Just don't forget to log the safety pilot's name, I recently read of a guy getting a violation from a FSDO for this...

I think the OP took off under IMC conditions using his IFR rating. So no safety piot was required. When he entered VMC and donned a hood, the passenger evolved (his word)  into a safety pilot.

Precisely @JScarry. The purpose of this question is to address a long XC my safety pilot and I would take (he flies there, I fly back and we reverse roles as left seat occupant). In the event of below VFR weather at the end of the day, I would be the one filing a plan, taking off, flying through the IMC part en route, and (presumably) emerging into VMC conditions at the later stages of the voyage.

I understand that. My answer is based on the scenario you describe.  The reverse holds true as well:  If the VFR pilot was flying a leg and the wx forecast went to IFR, the IR pilot could get an airborne clearance and take over as PIC.  No need to formally “declare” who the PIC is, just log what you actually did.

P.S.  at least I THINK I understand that...  I am open to constructive criticism if I have misunderstood your concerns, but in the absence of any requirement to declare safety pilot ahead of time it is clear to me that a crew could make these decisions on-the-fly as long as they log it correctly afterwards.  Rated pilots swap controls regularly, right?  This shouldn’t be any different.

The one caveat I will add is that if the VFR pilot’s name is on a VFR flight plan and you later need a pop-up IFR clearance the IR pilot isn’t associated with the new clearance.  It could get sticky if there was an incident, but I don’t think there is anything illegal about it.


text:
Can the Apache detect infrared (IR) lock?
Can the Apache, regardless if it's the AH-64E/D (US) or AH1 Longbow (UK), detect IR lock?
I am aware that the Wildcat AH1, Merlin HC3/4 and AH1 Longbow share the same defensive systems that can detect IR missile launch. However, I have yet to find any information suggesting any of these aircraft can detect an IR lock from a fire control system of another aircraft.

It's quite likely that this is simply a secret and that's why you can't find a definitive answer...  Sometimes the best thing to do with a game is to just "fudge it".  If you think having that capability would make the game more interesting, go ahead and put it in there.  Heaven knows, you wouldn't be the first person to fudge a bit in a military simulator :)

Quite possibly. Anyway, I think I answered my own question :)

I think I have answered my own question from a little bit of research.
Warfare systems such as Laser and Radar are detectable because they are active emissions (i.e. They have to make their own emission, wait for it to reflect back, then lock onto it).
Visual and Infrared are not easily detectable because they are passive. The IR Launcher or TV-Guided missile only requires the targets emission to lock onto, not its own in the example above, so there is no way you can detect being locked onto.

I don't have enough info for a full answer, but Peter Kampf has previously contradicted your "no way you can detect being locked onto statement."  https://aviation.stackexchange.com/a/22081/3146  I was surprised enough to put the following into my notes:  "Oh my god--IR missiles have cooled seekers and this is visible to an IR camera."  Not sure if that holds for all generations of IR missiles, but was definitely true of missiles like Stinger and the early Sidewinders.

Back-of-the-envelope calculations make me think that, while possible, detecting a cooled seeker is quite impractical IRL. The required resolution, FOV and processing needs of the system would make it quite an investment. I have been unable to find any literature supporting the development of such an "IR lock detector", as opposed to more general misile approach detectors.

@Peter's answer to the other question is actually not a contradiction. He's talking about devices that detect the presence of a missile, not determining if it's locked on or not. Countermeasures assume it's locked on, and deploy anyway. Better safe than sorry.

This answer is correct. There is no way to detect an IR lock, its not just hard, its impossible, as there is nothing to detect.

I think that I've been sufficiently told that I'm incorrect, and I believe it.  If you think that Peter's answer is incorrect, perhaps leave a comment on it

No. IR threat warning systems detect the energy from the missile.

It took me a little Googling, but I found one:  the Netherlands intends to equip their AH-64Ds with the AN/AAR-57A(V)7 Common Missile Warning System, a system that's capable of detecting infrared missile launches.  The CMWS can be used in concert with systems like the AN/ALQ-212 to actively jam incoming infrared missiles.
Googling for "Apache missile warning" seems to indicate those units are in widespread consideration or use.

Missile launch happens after the seeker has locked on. The question is about the latter, not the former.

Ah, fair enough. Maybe other people will make the same mistake and so the answer might still be useful to someone, but I accept the downvotes.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why are 'ghost flights' necessary?
This article details the recent (March 2020) grounding of 90% of Ryanair's fleet due to the COVID-19 outbreak.

Flight tracking data showed that all bar one of the jets had been flown in recent days: 35 had made loops of the airport, while the remaining 11 aircraft had operated a service at least once every four days.

Why are these flights required? The article states this is to keep the aircraft 'serviceable', but the airport I'm learning at has planes that haven't been in the air for months... if they are booked for a lesson, they get a service and away we go.
Why would a budget airline want to spend so much money on fuel and flight crew for these flights, when this could continue for months, it seems like it would make more sense to keep them grounded, and then service them all when this epidemic is over.

Passenger airplanes transport cargo as well and since so many of them are grounded, there are not enough cargo airplanes to satisfy urgent transportation needs. Some airlines therefore operate ghost flights without passengers for freight only. I don't know whether this applies to Ryanair though.

In Europe, an airline looses a slot if they don't use 80 % of it in a certain timeframe ("use it or lose it" rule). So some planes are operated just to keep the slots. This rule is, however, currently suspended (or at least being discussed) to avoid such ghost flights due to the Corona virus. See also https://www.businessinsider.de/international/coronavirus-airlines-run-empty-ghost-flights-planes-passengers-outbreak-covid-2020-3/?r=US&IR=T

@svoop Then that wouldn't be a ghost flight, it'd be a cargo flight.  You can run cargo in passenger jets, in fact it's a good plan for heavier pallets.  90% of the time a semitrailer "cubes out" before it hits weight limits; that number is way lower for aviation.  So you put the heavy cargo on passenger liners in their limited cargo holds. Now all the planes "cube out".

Airliners are both larger and more complex than the small aircraft you're familiar with at your local flight school. For an example of some of the items to consider, see: What do you need to do to bring a 737 Max back in service after 6 months in storage?
A lot of those things won't be improved just by flying the plane periodically, but some items are. Tires can develop flat spots from sitting for too long. Engines and systems need to have their fluids circulated. Getting things warmed up and moving helps to prevent corrosion. Even with proper storage procedures, an aircraft would have to be thoroughly checked for any foreign debris or damage that could have accumulated.
As the article you linked states:

Planes that have been grounded for a significant period have to be checked over before they are cleared to fly again, a process that keeps them from flying for even longer and costs the airline money.

There is of course a tradeoff between paying to put the aircraft in long-term storage, and later to bring them back into service, versus keeping them in working order. Also, as mentioned in the answer to the linked question, the flight crew need to fly a minimum amount to be considered "current" and allowed to fly passengers. Even aside from regulations, having periodic practice will help to maintain skills for everyone involved.
Having crews do a few laps around the airport helps to keep both the airplane and crew in working order, and avoids having to do more rigorous checks to get them back up to speed when needed, which can save both time and money.

"Airliners are both larger and more complex than the small aircraft you're familiar with" -- that's true but, frankly, all of the same things still apply to the smaller airplanes. There is a noticeable increase in net maintenance costs even for small planes flown monthly vs. those flown at least once a week. I don't know where the OP is flying or what "they get a service" entails, but I wouldn't trust an airplane that's been sitting on the ground "for months" to be ready for me to just hop in and go. ...

... Same thing applies to wheeled vehicles and boats, for that matter. Sitting idle is very bad, and if one is going to leave them idle for extended periods of time, it's cheaper in the long run to put them into storage properly. Conversely, if you want to make sure you're ready to resume operations immediately, it's better to just keep operating them.

@PeterDuniho You're right and to illustrate: In France, all non-essential VFR are currently forbidden for the duration of COVID-19 related restrictions. However, the DGAC (civil aviation directorate) allow flights on small airplanes if the maintenance manual demands them. (Further restrictions such as a mandatory flight plan apply.)

Some of this could theoretically be mitigated without actually flying though.  Tires can be saved from damage just by taxiing a few feet every now and then.  And you can start the engines up and run them for a while without actually taking off to keep them in decent condition (circulating oil, burning off collected dust, etc.)  Obviously the pilots need to practice to keep their skills from going rusty, but this could be done in a simulator.  It's certainly not ideal, but a heck of a lot cheaper, especially since nobody's travelling right now...

@Darrel:  "you can start the engines up and run them for a while without actually taking off to keep them in decent condition" -- not really. Most small airplanes use air-cooled engines. To operate them long enough to warm up the oil, evaporating accumulated moisture, keeping the engine warm for long enough to really do it properly, it's safest and easiest to just fly the plane, which keeps adequate cooling air moving over the engine. And while simulators light plane pilots have access to are great for procedures, they aren't all that good for basic operational skills.

@PeterDuniho Yeah, but we're not talking about small planes, are we?  These are commercial airliners.  Note: I am not a pilot or mechanic, my knowledge only comes from developing maintenance simulators for a while.

@DarrelHoffman, large airliners also have parts you can't meaningfully exercise while on the ground -- the landing gear retraction mechanism, for example.

@DarrelHoffman Once you get a Turbofan engine (like a commercial airliner) up to temperatures to properly warm up the oil, burn off moisture, et cetera, it will want air going through it at at least 300mph, for at least half an hour - good luck managing that on the ground!  This is similar to how a diesel car requires a fairly long journey (30 mins at 50mph) for the DPF to be able to get hot enough to "regenerate" successfully.  (Making them bad for "city drivers" doing lots of short or slow trips instead)

You can do that on the ground, but your neighbors will hate your guts.

@PeterDuniho : yeah, modern planes are more finicky than the good old An-2, which you could just leave out in the mud and rain and snow for half a year, and then start it up again with minimal fuss.

@Mark: You can exercise the landing-gear actuators just fine on the ground, as long as you put the aircraft up on jacks first.  (For that matter, with some aircraft, you can do that even without the jacks, but that tends not to be good for the aircraft.)

Perhaps this adds little to the answer already posted, but I feel it needs to be emphasized that
airliners are designed to fly.
Designed to fly a lot, in fact. Like, spend a significant portion of their working lives in the air. Southwest Airlines, for example, has each of its 737s in the sky for 9 hours a day. I imagine Ryanair's number is similar. And most of that time on the ground is spent moving as quickly as possible to do the tasks required to get back into the air again. Basically, having your fleet sit around is an off-design condition.
Not only is it an off-design condition for the aircraft itself, it's an off-design condition for the entire maintenance concept and infrastructure of the airline. An airline knows how to put airplanes in the air and keep them there as much as possible, because that's how to make the most money. (If you're an airline, of course; aviation is generally not the way to make the most money.) Airlines are not experts at parking large numbers of big airplanes for a long period of time and then returning them all to service. In fact, no one is because, in general, this situation just doesn't happen.
So, your choice is either go through the process of mothballing your airplanes for an indeterminate period, which involves a bunch of maintenance tasks you're not equipped for (not to mention finding a place to put them) or that you'll have to pay someone else to do (likely at a premium right now), or try to keep the fleet operating as close to the design condition as is reasonable. The former option has the added drawback that the airplanes are likely to be a bit cranky for a while (i.e., more unexpected problems) after coming out of storage. The latter option has the added benefit of keeping flight and maintenance crews more current.
We can even run some rough numbers. Based on the article, let's say each airplane currently flies about an hour a day rather than nine. That means it might be due for what amounts to an A check every year or so, which at the high end could take 100 maintenance hours performing tasks that the airline does all the time and has the people and materials in place for. Compare to the process of mothballing and then unmothballing an airplane, which might take at the low end 200 hours of tasks that are not often performed. Of course in the interim the cost of flying is greater than the cost of sitting, but still it could be cheaper for an airline to run these "ghost" flights for quite a while than put their fleet in storage.
Overall, it is simply a less financially risky proposition at this point to give the airplanes a little bit of time in the air every once in a while than ground them and expect to resume service quickly. Flying and maintaining them "as usual" presents a known situation for an airline, especially when the horizon for returning to normal is closer to months than to years. Storing the aircraft for what could potentially be a relatively short period (as far as these things go) is fraught with unknowns.

Hey, I enjoyed the million dollar blog post. Thanks for that and the answer!

I'm pretty sure the ryanair number for plane utilization is higher than nine hours a day. Couldn't find a recent source though.

@bobsburner: Could the difference be between "in service" (including turn-around time on the ground) and "in the sky"? 9 hours per day in the sky sounds reasonable enough for a 737 on domestic routes. That could easily translate to 16+ hours in service, as you have a lot of loading/unloading time when you fly many short hops.

In addition to all these great breakdowns of the technical aspects of planes airlines will lose their precious airport-slots if they fail to actually use them.
I.e. if an airline pays for a (lucrative, useful) time-slot & terminal at a certain airport, but then doesn't actually use it, the airport will give away the slot to someone else.
Therefore there are occasional empty flights just to keep up the slot at the airport.
Source:

As far as I'm aware, just about everyone has waived the requirement for using timeslots right now.

Oh neat, I didn't know that! That'd mean the current ghost-flights at least are less motivated by airport-slots :)

One thing also to take into consideration:
Pilots do need to fly (and especially to land) regularly to stay current - both legally and also because these skills can degrade quite fastly.
This has been a significant issue in the hot days of the pandemic.

This was covered in several of the existing answers.


text:
What is this airplane I saw with propellers behind the engine and canards on the top of the plane?
While playing Pokémon GO, I saw a plane with:

Propellers behind the engine.
Canards at the tip of the plane.
Normal-looking tail with a flat wing at the end of the upright bit.

I know these are probably not the correct terms, but I'm not sure what else to call those components.

Could it be a VariEze? https://en.wikipedia.org/wiki/Rutan_VariEze

The terms you're looking for: "Propellers behind the engine": this is a pusher configuration.  "Normal looking tail with a flat wing at the end of the upright bit": this sounds like a T-tail.

The "propellers behind the engine" is called a "push configuration". One you look through aircraft that are private business planes, the Piaggio P.180 Avanti comes up as a likely contender.

The stabilizer arrangement here is usually called a "three-surface" -- both canard and conventional stabilizer in addition to the main wing.  There are a number of current and next generation jet fighters with this layout, as well, though of course they don't have pusher propellers.

Could have been a Beechcraft Starship too, I don't have a picture on hand. Large plane or small?

The Starship does not have a "normal looking tail", though.

@CrossRoads I'm begining to wonder if that was it? Picture.

The second thing on the Starship ID checklist after the rear-facing engines, is the winglets.  This has none.


text:
Can I join the Navy after a corrective eye surgery and still be a Naval Aviator?
I currently do not pass the requirements for uncorrected distant visual acuity according to the Navy physical standards document. However, if I were to receive eye surgery to correct my vision before joining and then apply to OCS/Flight School, would I be cleared as Class 1 aviation personnel and be able to fly as a Naval Aviator? Thank you!

(Here's some of the information from the linked pdf)
Class I: Naval Aviators and Student Naval Aviators (SNA). Designated Naval aviators are
subdivided into three Medical Service Groups based upon the physical requirements of their
specific flight duty assignment
Medical Service Group 1: Aviators qualified for unlimited or unrestricted flight duties
Medical Service Group 2: Aviators restricted from shipboard aircrew duties (include
V/STOL) except helicopter
Medical Service Group 3: Aviators restricted to operating aircraft equipped with dual
controls and accompanied on all flights by a pilot or copilot of Medical Service Group 1 or 2,
qualified in the model of aircraft operated. A waiver to medical Service Group 3 includes pilot-incommand
(PIC) authority unless PIC authority is specifically restricted.

Service Group 1, 20/100 or better each eye uncorrected, corrected to 20/20 or better
each eye.
Service Group 2, 20/200 or better each eye uncorrected, corrected to 20/20 or better
each eye.
Service Group 3, 20/400 or better each eye uncorrected, corrected to 20/20 or better
each eye.

The first time distant visual acuity of less than 20/20 is noted a manifest refraction (not
cycloplegic) shall be performed recording the correction required for the aviator to see 20/20 in
each eye (all letters correct on the 20/20 line).

Are you talking to a recruiter? It's usually a pretty easy question for them to answer. I went through the OCS/AFOQT tests, but washed out in MEPS for different medical reasons. There is a medical appeals process but I wasn't able to get it reversed in my case even though I didn't have the condition.

Hi Ron, thank you for the suggestion! I haven't been able to visit my local recruiter's office as it seems that it has been closed for some time. However I'm planning to visit one once I gather a little more information.

The USAF has allowed corrective eye surgery for pilots for a number of years and I believe the Navy has as well.  But you should get the latest policy directly as there may be limitations on the type of procedure (PRK/LASIK/?) that is acceptable.  You should also talk to an eye surgeon to determine your ability to have the procedure. Not everyone is capable of having the surgery.

That's true, as I'm still a student I may have to wait for my eyes to stabilize as well. I believe PRK is the more widely accepted option, but that will be something that I'll be sure to ask the recruiter as well!

I had this explained to me by an OSO a few years back. The answer is a qualified, yes, but the devil is in the details.
At the time, no procedure that involved cutting a corneal flap was approved. This means that LASIK and similar procedures were not approved for aviators. (This may change, but I think its unlikely). So that leaves PRK and similar procedures that only modify the the cornea's surface. This follows recommendations my medical professionals that recommend people that play contact sports to opt for PRK instead of LASIK.
However, here is the detail that was explained to me that I consider to be "the catch", you must already be in the Navy. In other words, you must have already made a commitment, then once inside, you can apply for the waiver and use a Navy approved opthamologist to perform the procedure. The problem with this is that if you are a person that is only interested in being a pilot, you must sign up for some other reasons (it might be aviation related, but not pilot) then once commissioned, then you can ask them to waive the rule and allow you to have vision correction surgery.
Also, at the time it was explained to me, you needed to wait for 1 year after the procedure before being considered for an aviator position. This is logical as they want to see if the procedure was successful and healed properly.
If you're already in the Navy this is great, but if you want to join the Navy for the sole purpose of being an aviator, I would look very closely at the details, and get it in writing before you commit.

Thank you for the information! I'm currently a student who is not in the Navy, but your response will help a lot for when I go talk to a recruiter. One thing that came to mind, do you happen to know why you must already be in the Navy? Is it because they want to be informed on every step of your procedure regarding the eye surgery?

@wow1881 I'm not sure, but I think you are correct. They want to be involved with every step of the process. Another thing to consider is that they have plenty of applicants that are perfectly qualified to be aviators that have uncorrected 20/20, so granting this waiver is sort of a perk for commissioned officers that want to be pilots who are already serving.

@wow1881 don't take everything the recruiter tells you as gospel, ask the recruiter to refer you to the rules pertaining to the laser eye surgery for aviators so that you can read it yourself. If it's different than what I said, please come back and update the answer so others can benefit from up to date information.

Ah that makes sense, I hadn't thought of that. And yes, good points regarding the recruiter. I've heard that sometimes they'll tell you varying levels of information to try to get you to join, so I'll be sure to follow your advice and ask for official documents! And if I find anything, I'll update the answer!


text:
What does "Last Call" mean on CTAF frequency?
At non-towered airports I sometimes hear pilot's using the CTAF use the term “last call” as they depart the traffic pattern. This is not listed in the AIM.
What information is this suppose to convey and should I care?
Does this have some meaning internationally that I don't know about?

Well OBVIOUSLY it means that after that point there will be no more beer served!

It means they are changing frequency and will not be making any more CTAF calls. As far as I know its not required although something along those lines is pretty common place. Personally I call:

Departing the pattern to the [north|east|south|west]

Its the self announce version of "frequency change approved"

I make a similar call: "Cardinal N12345 departing the area to the [N|E|S|W]"

Is "departing the pattern" preferred over, say, "exiting the pattern"? I'm only 10% of a pilot, but I think of "departing" as being a sort of euphemism for "taking off".

Ive have heard both, often on the ground you will also say "Cherokee taking 05 for a north bound departure". At an uncontrolled field an extra call or two is always better than an ambiguous situation.

The AIM suggests announcing, before taxing onto the runway for departure "Remaining in the pattern” or “Departing to the (...direction)”. Since that is the last call AIM suggests, it seems to me it makes no sense to repeat that after takeoff and just adds unnecessary radio noise.

@jwzumwalt  It is not approved phraseology and is the latest in pilot verbosity used to clutter the CTAF, If it follows the same arc as the vile "Traffic in area, please advise." we may see an update in the AIM similar to 4-1-9 g.1.which states "Pilots stating, “Traffic in the area, please advise” is not a recognized Self−Announce Position and/or Intention phrase and should not be used under any condition."


text:
Can I use dual time for the 10 night takeoffs and landings required in 61.129?
For the 5 night VFR hours and 10 T/O at class B/C/D required in 14 CFR 61.129(a)(4)(ii), can you mix/match solo and dual instruction (as PIC) time for these hours and landings? In other words, are they combinable? I may reach all 5 solo but definitely have more than 5 night dual (as PIC).
Also, does being under the hood dual with CFI count? I would expect not since you're not flying "the traffic pattern" (i.e. right base, straight in, etc.) but just wanted to get consensus.

Partially related

No being under the hood does not count as "night flying" see this question for the FAA's definition of night flight.
You dont need to be alone in the aircraft for these TO/LD's while the FAA definition of "solo flight" which this question covers could apply it does state that an instructor can be present

(4) Ten hours of solo flight time in a single engine airplane or 10 hours of flight time performing the duties of pilot in command in a single engine airplane with an authorized instructor on board (either of which may be credited towards the flight time requirement under paragraph (a)(2) of this section), on the areas of operation listed under § 61.127(b)(1) that include -

(ii) 5 hours in night VFR conditions with 10 takeoffs and 10 landings (with each landing involving a flight in the traffic pattern) at an airport with an operating control tower.

Perhaps the OP is thinking about the wording that follows the part you quoted: "or 10 hours of flight time performing the duties of pilot in command in a single engine airplane with an authorized instructor on board".

@Pondlife thanks for the note, i have updated accordingly

Thanks. Yes, so I guess just wondering if the term 'or' implies a mix-n-match accumulation of hours, or do the hours need to be done mutually exclusive? At least 10 hours solo or at least 10 hours dual instruction as PIC but can't add up both to 10?

Long story short, you can have an instructor on board if you want but you can't log the time as training. And you can be under the hood if you want, as long as you're under the hood at night, in VFR conditions, and you're not logging it as training time.

Here's the relevant wording from 61.129:

Ten hours of solo flight time in a single engine airplane or 10 hours
of flight time performing the duties of pilot in command in a single
engine airplane with an authorized instructor on board

And:

5 hours in night VFR conditions with 10 takeoffs and 10 landings (with each landing involving a flight in the traffic pattern) at an airport with an operating control tower

First, what about dual? "Dual" isn't an official FAA term but "training received" is and it means that an instructor endorsed your logbook to show that they provided training. So, does 61.129 allow you to use that training time? Well, by definition (61.51(d)) "solo" means that you're alone in the aircraft, so clearly "solo" and "training received" can't happen at the same time.
That leaves "performing the duties of pilot in command in a single engine airplane with an authorized instructor on board". According to the Kuhn (2014) legal interpretation, you can have an instructor on board but you can't log it as training received:

Because this flight time is a substitute for solo flight time, the
pilot is not receiving instruction and therefore cannot log this time
as dual instruction received. The pilot can log the time to meet the
requirements of § 61.129(a)(4) and log total flight time

Whether you want to pay a CFI to just sit there without you being able to log training time is up to you. The CFI can still log PIC time, by the way, according to the same interpretation.
Summing up the dual part, you cannot use training time as solo time. To meet the requirements in 61.129 you have two options: be alone in the aircraft, or have an instructor on board but not log any training time.
Second, what about hood time? "Night VFR conditions" describes the flight conditions but doesn't say anything about what happens inside the aircraft. I don't see anything that says you can't be under the hood with a safety pilot as long as you're also flying in night VFR conditions. In other words, being under the hood during daytime doesn't count: the requirement is to be in night VFR conditions.